Generally, a manufacturing process of a pneumatic tire includes a vulcanizing process for promoting a vulcanizing reaction in an unvulcanized pneumatic tire (so-called raw tire or green tire). In the vulcanizing step, an unvulcanized tire is vulcanized by using a vulcanizing apparatus provided with a tire vulcanizing mold for forming a tread part, a side wall part, a bead part or the like. Further, the tire vulcanizing mold has a bead ring for forming the bead part of the unvulcanized tire.
Here, the bead part includes an arc-shaped bead heel part formed to be protruded toward the outside in a tire width direction and therefore the bead part has a complicated shape. Thus, when the unvulcanized tire is subjected to vulcanization molding in an inner surface of the bead ring in order to vulcanize the unvulcanized tire stored in the tire vulcanizing mold, air might be sealed between the bead heel part and the bead ring without being released. In such a case, air retention called bare is generated on a tire surface and therefore appearance of the tire might be spoiled.
As a solution to this problem, a technique of discharging air by disposing a vent hole on the bead ring is utilized. However, when adopting such a technique, rubber of the unvulcanized tire is entered into the vent hole and many spews are generated on the tire surface in the vulcanizing process. Such spews are cut and removed for improving the appearance, however much time is needed for the removal operation and a part of the spews might be left without being removed. Especially, since the bead part has a complicated shape, the spew is apt to be remained, and this configuration not only spoils the appearance but also deteriorates adhesion between the beat part and a rim, and as a result of that, an air leaking of a tubeless tire might be occurred.
Further, when the bead ring is repeatedly used, a rubber crumb or a mold releasing agent is gradually stored in the vent hole, and such a configuration leads communication failure of the vent hole which prevents air from being exhausted. Thus, a washing operation of the beat ring for removing the rubber crumb is needed. Such a washing operation needs much time and deteriorates productivity because of increase of a manufacturing stopping time in accordance with the washing.
In order to solve such a problem, a tire vulcanizing mold in which a bead ring is divided and a plurality of thin plates (shim) is arranged on a divided surface of the bead ring at intervals in a tire circumferential direction is suggested (see Patent Literature 1).
According to such a tire vulcanizing mold, a gap for air bleeding can be ensured over the whole periphery of the bead ring in the tire circumferential direction without forming the vent hole, and this configuration can eliminate the need for performing the removal operation of the spew, and it is considered that productivity in manufacturing a tire can be improved.